Improvements in or relating to protective arrangements for three-phase a.c. distribution system

摘要

555,328. Protective cut-out arrangements. REYROLLE & CO., Ltd., A.. and HARLE, J. A. Feb. 12, 1942, No. 1887. [Class 38 (v)] An arrangement for protecting a three-phase circuit against overload and single-phasing comprises, in each phase, a high-breaking capacity fuse CSP1/SP ... CSP3/SP, and a normal trip coil ESP1/SP ... ESP3/SP operative on trip mechanism D of a low-breaking capacity circuit-breaker B having its contacts in series with the respective fuses, the operating times being such that the breaker deals with overloads up to, say, ten times normal load, whereas the fuses open overloads in excess of that figure. When a fuse blows, single-phasing is prevented by an auxiliary trip coil FSP1/SP ... F' in shunt therewith operating the mechanism D to clear the circuit. The shunt impedance is such that each coil is inoperative while the fuse is intact, but operates with the minimum voltage likely after blowing of the fuse The fuses may be withdrawable for isolating the breaker, the trip circuits being also isolated at contacts HSP1/SP ... HSP3/SP. Switch mechanism interlocking with lids. The circuit-breaker B and fuses C are mounted in cases L. M. Fig 3, containing the auxiliary trip coils (not shown). When the handle G is lowered to open the breaker, the rod Q disengages a lug QSP2/SP on door MSP1/SP, so allowing access to the fuses. A rod O carried on arms OSP1/SP is rotatable clockwise for permitting removal of all the fuse holders N, and is then urged by spring OSP2/SP into a position in which rod P frees a lug P' on door LSP1/SP, so enabling inspection of the breaker itself. Thus the fuses cannot be removed until the breaker is open and the breaker cannot be inspected until isolated at the fuses. The shape of lugs PSP2/SP, QSP2/SP prevents movement of P, Q while the doors are open. Lugs P', Q' on the casing walls guide the rods P, Q. The Specification refers to oil-immersion of the apparatus and to other modifications of details, and to Specification 549,376.